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Business Segment Information - Intercompany Segment Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net revenues	$ 201,728	$ 204,625	$ 368,551	$ 368,887
Intercompany revenue for P&A work			5,327
Droshky Prospect
Segment Reporting Information [Line Items]
Intercompany revenue for P&A work			5,300
Well Intervention
Segment Reporting Information [Line Items]
Net revenues	159,074	161,759	281,305	291,328
Robotics
Segment Reporting Information [Line Items]
Net revenues	45,446	39,060	84,487	66,229
Intercompany Eliminations
Segment Reporting Information [Line Items]
Net revenues	(18,413)	(12,537)	(28,115)	(21,334)
Intercompany Eliminations \| Well Intervention
Segment Reporting Information [Line Items]
Net revenues	(9,812)	(4,215)	(13,037)	(6,167)
Intercompany Eliminations \| Robotics
Segment Reporting Information [Line Items]
Net revenues	$ (8,601)	$ (8,322)	$ (15,078)	$ (15,167)